I'm also a Rainlendar Pro user -- was using Remember The Milk to sync Rainlendar with my iPhone but since the free version only let's you sync to iPhone once a day I moved to toodledo. I'm currently using toodledo to display the tasks in Rainlendar, but would love to have full API sync support someday.

I know there is one-way syncing using toodledo's url .ics feature, but can you explain how to make it possible to create/edit todo items on Rainlendar that get synced to toodledo? It might be good to have a stop-gap solution for the time being, even if it is a little messy.